A rash of sea otter deaths attributed to parasites may have its roots in the increasing urbanization of the California coastline.

Researchers believe that the parasites are being washed into coastal waters around Morro Bay and the Monterey Peninsula in the feces of cats and opossums, two animals that thrive in suburban areas. The parasites enter the marine food chain and ultimately end up infecting and killing otters, a threatened species.

If that theory proves correct, solutions will not be easy, experts say, given the fact that both cats and opossums are tenaciously rooted in the state's suburbs. Eliminating opossums may be possible in some areas, but not eliminating cats. So for now, experts are relying on a campaign to educate the public about the threat.

"We need to portray sea otters as sentinel animals," said Patricia Conrad, a UC Davis parasitologist. "We know these parasites are abundant in the environment. They represent a human risk. Animals are getting sick from them, and cat feces appear to be the link, so it certainly would be desirable to reduce cat feces in the environment.

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"Sea otters are a red flag, and we need to help people see that, to make them aware of the basic problem," she said.

California sea otters, virtually wiped out by fur hunters by the turn of the 20th century, were on the rebound until the mid-1990s. But since a population peak of 2,400 in 1995, their numbers have fallen to about 2,000 otters today. In the past four months alone, about 100 have died.

PROTOZOANS, PARASITE BLAMED

A recent UC Davis study found that two protozoans -- Toxoplasma gondii and Sarcocystis neurona -- were responsible for an increasing number of California sea otter deaths. Another parasite that lives in sand crabs, which otters sometimes eat, also was implicated in some deaths.

While Toxoplasma and Sarcocystis infect a wide variety of animals, only two species transmit infective "cysts" in their feces -- house cats for Toxoplasma,

and the Virginia opossum for Sarcocystis.

No firm parasite transmission routes from terrestrial animals to otters have been established, but researchers think contaminated cat and opossum feces could be accumulating in backyards, parks and vacant lots throughout the year, to be ultimately flushed into coastal waters during winter storms.

The infective cysts then could be present in tidal waters and ingested by filter-feeding clams and mussels, or they might attach to algae and be consumed by abalone. The otters probably are infected by the parasites when they eat the shellfish, which are among their preferred foods. The study found high incidences of sea otter infection near freshwater outfalls.

DANGERS OF POPULATION GROWTH

The UC Davis study has particularly ominous implications for the state's surviving sea otters because the populations of both cats and opossums expand with human population: Suburbs are their preferred habitat.

Cats, of course, share homes with humans in high numbers, and there are large colonies of feral cats, many supported at feeding stations tended by animal fanciers. Opossums -- not originally native to the West Coast but now one of California's most populous wild mammals -- thrive in backyards, empty lots and even traffic medians.

"You never find them in the deep forest," MacKay said. "Whenever you start carving up woodlands, you expand the amount of opossum range logarithmically, since you're creating all that edge habitat."

From this perspective, he said, "suburbs are very legitimate habitat -- they constitute huge areas of wooded edges."

What can be done?

"You'd have to give (any major action) a lot of thought," said Conrad, the UC Davis parasitologist. "Before you jump in, you have to gain public support, and for that, you need the appropriate scientific data. We don't have that yet.

"We're certainly not going to eliminate cats -- they're part of our society.

What we need at this point is a means of finding common ground between wildlife advocates and cat owners. Anything else is impractical," Conrad said. For the immediate term, public education is the best approach, she said.

Some pet pundits worry that marketing trends in cat litter might be exacerbating the problem.

"In the past few years, we've seen this tremendous boom in biodegradable litters made from things like wheat straw and alfalfa," said Elaine Perednia, who runs a pet-sitting enterprise in San Francisco. The selling point for these products is that they are flushable and environmentally benign.

"More and more cat owners are switching to them, since they can clean out their cat box straight to the toilet," Perednia said. "Just from what I've seen, the amount of cat litter being flushed is enormous. The environment must really be getting bombarded with it."

Since the UC Davis report was released, Perednia said, she has advised her clients to bag soiled litter and deposit it into garbage cans for transport to sanitary landfills.

OTHERS BLAME POLLUTED RUNOFF

But some sea otter authorities question the conclusions of the UC Davis report and say that it addresses only part of the problem. Polluted runoff from the Central Coast's expanding cities and suburbs, they say, is affecting the otters directly, making them more susceptible to parasitic infection.

Steve Shimek, director of the Otter Project, a Monterey group devoted to the recovery of California's sea otter population, said that a study by the National Wildlife Health Center, an organization associated with the U.S. Geologic Survey, found Toxoplasma and Sarcocystis were responsible for only 8 percent of otter deaths.

"That was recently revised to 25 percent, when otters that had died of shark attack were reassigned as parasite deaths if Toxoplasma or Sarcocystis was found during necropsy," Shimek said. That kind of methodology is dubious, he said, because it cannot be proved that parasitized otters become so dazed that they automatically fall prey to sharks.

"An otter that dies of shark attack should be listed as a shark attack victim," he said.

On the other hand, Shimek said, "What we do know with certainty is that otters carry toxic loads of chemicals such as DDT, PCB and butyltins, a direct result of runoff from our urbanized coastline." Shimek said such chemicals are known to suppress the immune system.

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What otters require, Shimek said, is a plan for better sewage treatment infrastructure.

"We need plants that treat sewage to the point that all pathogens are killed. We need to eliminate sewage overflows, which are all too common on our coast. And we need to build buffer zones around waterways and the coast to handle nonpoint source pollution (runoff). The longer you can retain chemicals and pathogens in the soil, the more they'll degrade. We have to slow their distribution into the aquatic environment."

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